The present invention relates to lightning arresters having active resistor cores formed of zinc oxide.
In electrical engineering, the former, classical lightning arresters based on silicone carbide are being replaced by those based on metal oxides. The resistance material based on ZnO plays an outstanding part in this. The conventional designs use as a rule--from certain voltages upwards--stack-like cores, composed of individual discs, made of voltage-dependent sintered resistance material (varistors). Such cores are known from numerous publications (cf. for example U.S. Pat. No. 4,335,417, DE-A-No. 2 934 832, CH-A No. 626 758). The height of the disc used is limited (e.g. to 60 mm) and the height to diameter ratio is generally less than 1.
Such stacks composed of individual resistance discs are, by their nature, not self-supporting and must therefore be braced, fitted or cast into an insulation housing or otherwise fixed in some way. At the same time, the heat developed during operation must be led away to the outside through the insulating housing.
The stack-like configuration of a conventional lightning arrester is--particularly at higher voltages and power ratings--expensive and complex and also incorporates additional risks due to the numerous internal contact areas.
It has already been proposed to embed a sintered rod-shaped ZnO resistor core in a porcelain mass and sinter the latter at a relatively low temperature into a solid insulator firmly connected to the resistor core. Such a connection between resistor core and insulator can be made without radial gap (cf. EP-A-No. 0 004 349). This already represents a simplification of the design compared with the stack-like configuration of usual arresters.
However, there is the general need to simplify further the configuration and the production of lightning arresters based on ZnO varistors and to make them suitable for mass production.